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    <script>
        /* <,>,<=,>=，==,!= 
        返回的是boolearn*/
        var a = 10;
        var b = 20;
        console.log(a == b);
        console.log(a != b);
        var str1 = "new";
        var str2 = "xin";
        console.log(str1 != str2);
        console.log(a != "true");
        // NaN和任何数据做！=比较时，始终返回true
        // isNan
        console.log(isNaN(b));
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